Method of and apparatus for grinding material



4, 1965 w. WIELAND 3,202,364

METHOD OF AND APPARATUS FOR GRINDING MATERIAL Filed Oct. 25, 1962 INVENTOR. Walter Wielcmd Attorneys United States Patent 3,202,364 METHOD OF AND APPARATUS FOR GRENDING MATERIAL Walter Wieland, Aargau, Switzerland, assignor to Cemeutfahrik Holderbank-Wildegg A.G., Holderhank, Aargau, Switzerland, a corporation of Switzerland Filed Get. 23, 1962, Ser. No. 232,436 Claims priority, application Switzerland, Nov. 3, 1961, 12,691/ 61 9 Claims. (Cl. 24130) This invention relates to a method of and an apparatus for grinding material by means of movable grinding elements.

It is known to comminute and grind material in containers by means of grinding elements, which are set in motion in such a manner that under the influence of gravity they perform the desired grinding and comminuting work. This is effected for example in ball or tube mills in which a mixture of material for grinding and grinding elements is moved in such a manner owing to the rotation of the mill that the grinding elements are lifted upwards to a certain extent in the direction of rotation, whereupon they fall down and in so doing comminute the material.

It is also known to provide in the rotating container a stirring device which rotates relatively to the container, in such a manner that on the one hand the rotational movement of the container causes the material and the grinding elements to accumulate in a layer along the container wall owing to the action of centrifugal force, and on the other hand the stirring device obliges the grinding elements to be displaced relatively to one another.

However, such mills have the disadvantage that the pressure with which the grinding elements are pressed against one another depends on the magnitude of the centrifugal force.

Thus, in order to obtain a strong grinding action, it is necessary to make the container run at a high rotational speed. But even then the pressure only increases gradually from nil towards the outside owing to the internal free surface of the layer of grinding elements, and the full pressure is reached only in the vicinity of the external wall of the container.

This disadvantage is obviated according to the present invention in that in a layer formed of grinding elements and filling the space between two walls a relative movement of the mutually contacting grinding elements is constrainedly brought about by relative movement of these walls relatively to one another in the tangential direction.

Whereas in the case of the known apparatus with stirring devices the grinding elements can be displaced in opposition to centrifugal force at the internal free surface of the layers when the stirring device is operated, in the present case the fact that the layer of grinding elements is bounded at both sides by the walls which move relatively to one another prevents the grinding elements from escaping. At the relative movement of the walls with respect to one another a pressure is produced in the layer of grinding elements which is greater in proportion as the space between the walls is more densely filled with grinding elements or the material to be ground.

Therefore, in contrast to the operations carried out in conventional ball and tube mills, in the present case the material is comminuted not by the impact energy of the balls impinging on the said material, but by a rub hing-down action between the grinding elements on the one hand and between the particles of material themselves on the other hand. A good grinding elTect is obtained if many grinding elements are displaced relatively to one another with considerable pressure and there are large frictional contact surfaces between the grinding elements. The grinding material is subjected mainly to shearing and compressive forces, thus improving the economical aspect of the comminution, but destruction of the grinding balls and grinding plates by impact and also formation of undesirable slabs in the finished product are avoided.

An example of embodiment of an apparatus for carrying the method according to the invention into effect is illustrated in a simplified form in the accompanying drawings. The method is also explained by Way of example with the help of this apparatus.

In the drawings:

FIGURE 1 is an axial longitudinal section through the apparatus,

FIGURE 2 is a section on the line Il1I of FIGURE 1, and

FIGURE 3 is an axial longitudinal section through another form of embodiment.

The mill illustrated in FIGURES 1 and 2 has two drums which are arranged co-axially with respect to one another, namely an outer drum 1 and an inner drum 2. These drums 1, 2 bound an annular chamber 3 externally and internally, respectively. In the axial direction, this chamber 3 is closed by the end plates 4 and 5 which carry the drum 1 and are provided with central apertures.

The drum 2 is arranged within the container formed by the drum 1 together with the end plates 4 and 5. It is carried by end plates 6, 7 which are provided with hollow stub shafts 8 and 9 respectively. The stub shaft 8 passes through the central aperture in the end plate 4 and is supported in a bearing 10. A bearing 11 is provided for the stub shaft 9 which extends through the central aperture in the end plate 5.

Interposed between the end plates 4 and 6 of the drum 1 and the stub shafts 8 and 9 carrying the drum 2 are ball bearings 12 and 13 respectively which permit relative rotational movement of the drums 1 and 2 with respect to one another. The drum 1 is driven by means of a gearwheel 14 which is connected to the end plate 4 and which itself is driven through the agency of a pinion 15 by driving means generally indicated by a motor 15 Mounted on the stub shaft 9 is a gearwheel 16 which meshes with a pinion 17. Through the agency of this pinion, the drum 2 can be driven by means generally indicated by a motor 17 at a rotational speed which differs from the rotational speed of the other drum, or it can be held fast by a brake 17 The chamber 3 is filled with grinding elements 18 in the form of balls which form a layer disposed annularly about the drum 2 and contacting the drum 1 and also the drum 2. The material to be ground is introduced through the hollow stub shaft 8, first of all passes into an inlet space 20 bounded axially within the drum 1 by the end plate 6 and a partition Wall 19 and thence through apertures 21 formed in the drum 2 into the annular chamber 3, i.e., into the grinding chamber. The ground material is passed through apertures 22 formed in the vicinity aaoasea of the end plate '7 in the drum 2 into an outlet space 24 which is situated within the drum 2 and is bounded in the axial direction by the end plate 7 and a further partition wall 23, and the said ground material is discharged thence through the hollow stub shaft 9. In the same way, air can be blown through the apparatus for cooling and conveying purposes.

During operation, the relative rotational movement of the drum 1 with respect to the drum 2 is maintained either by rotating the drums l and 2 at difierent speeds in the same or in opposite direction or by rotating only one of the drums while the other drum is held fast. The drums 1 and 2 thus form two walls parallel to one another which carry out a relative movement with respect to one another in the tangential direction. Owing to friction between the grinding elements and these walls, the grinding elements contacting one another are constrainedly given a relative movement with respect to one another in the layer formed of such grinding elements 18 and filling the chamber 3 between these Walls.

In order to guarantee that this effect is obtained to an adequate extent, the drums I and 2 are provided at their surfaces facing toward the grinding elements 18 with projections for increasing friction, these projections consisting in longitudinal ribs 25 and 26 respectively. However, instead of these ribs it would also be possible to use different types of irregularities at the drum surfaces. In view of the centrifugal forces acting upon the grinding elements in the sense of lowering the surface pressure at the inner drum, the projections 26 provided at the inner drum 2 are of particular importance.

Owing to the fact that the grinding elements are obligated to be displaced relatively to one another in the peripheral direction of the drums 1, 2, when the chamber havingto make use of centrifugal force. The intensity of the grinding pressure can be influenced by varying the amount of filling, and in this way can be adapted to the grindability of the material. The more densely the grinding chamber is filled with grinding balls or material, the greater does the grinding pressure become.

It is expedient to operate the apparatus in such a manner that one of the two drums, for example the outer drum 1, is rotated whilst the other drum is held fast. This other drum can hereby be fixedly mounted. In order to avoid considerable starting moments when the apparatus is brought into operation, in the embodiment illustrated in FIG. 1, however, the releasable brake 17 is provided for the inner drum 2. Then, when startingup, this brake 17 will first of all be released, so that the inner drum 2 can co-rotate freely with the outer drum 1. Only after the working speed is reached, the inner drum is braked to a standstill by fastening brake 17 the drive then being subjected to load from the considerable frictional forces produced by the relative movement. The apparatus can also be operated with the inner drum being 'rotated and the outer drum being held fast.

The constructional form shown in FIGURE 3 shows fundamentally the same layout as that shown in FIG- URES 1 and 2. The only difference is that in this constructional form the inner drum 2 is cooled by means of a cooling liquid.

An annular wall 27 arranged within the drum 2 forms with the partitions I9 and 23 a cooling jacket 22; which is connected to a source of cooling medium (not shown) by a pipe 29 extending through the stub shaft 9. A pipe 3t) which is led through the stub shaft 8 and is arranged at the opposite side discharges the cooling medium from the jacket 28. In this way effective cooling can be obtained even with a high grinding output.

The illustrated apparatus is also suitable for self-generated grinding, relatively large pieces of the material to be comminuted being used as grinding elements.

Cit

What is claimed is:

l. The method of grinding material comprising the steps of forming a layer of movable grinding elements in an annular space whose inner and outer peripheries are defined by a pair of radially spaced, coaxial, circular cylindrical walls; accelerating said wails at the same rate to the same predetermined angular velocity about their longitudinal axes; braking one of said walls to thereby bring it to rest and produce relative movement between the grinding elements; admixing the material to be ground with said layer of grinding elements so that it is ground by the relative movement of those elements in relation to one another; and discharging the ground material from said layer.

2. An apparatus for grinding material comprising a pair of walls spaced from each other to define an intervening space of substantially uniform thickness; means closing opposite ends of said space; a layer of movable grinding elements filling said space, part of said elements being situated immediately adjacent one of said walls, another part being situated immediately adjacent the other of said Walls, and the remaining part being situated between said first named parts; means for moving said walls relatively to each other in the tangential direction; projections carried by at least one of said walls and penetrating into said layer to the depth of the grinding elements situated immediately adjacent the wall so as to prevent movement of the last named grinding elements relatively to the adjacent wall in the tangential direction; and means for adding the material to be ground to said layer and for discharging the ground material from said layer.

3. An apparatus for grinding material comprising inner and outer drums having coaxial surfaces of revolution spaced radially from each other to define an intervening annular chamber; means closing opposite ends of said chamber; a layer of grinding elements filling said chamber, an inner part of said elements being situated immediately adjacent the inner drum, an outer part being situated immediately adjacent the outer drum, and the remaining part being situated between the inner and outer parts; means for rotating at least one of said drums so as to effect relative rotation with respect to the other drum; projections carried by at least the inner drum and penetrating into the layer of grinding elements to the depth of the grinding elements situated immediately adjacent the drum so as to prevent displacement of the last named elements relatively to the adjacent drum in the circumferential direction; and means for adding the material to be ground to said layer and for discharging the ground material from said layer.

4. The apparatus defined in claim 3 in which both drums are rotatably supported; one of said drums being provided with motor means and the other drum being provided with a releasable brake.

5. The apparatus defined in claim 4 in which the drum provided with motor means is the outer drum.

8. The apparatus defined in claim 3 in which the in- I terior of the inner drum comprises partitions extending in the transverse direction of the drum axis so as to form an inlet space for the material to be ground axially at one end of the inner drum and an outlet space for the ground material at the opposite end; the said inner drum being provided with perforations establishing communication between the annular chamber which contains the layer of grinding elements and said inlet and outlet space, respectively; and said inner drum being further provided with hollow shaft ends serving for the supply of the material to be ground to said inlet space and for the discharge of the ground material from said outlet space.

9. The apparatus defined in claim 8 in which the inner FOREIGN PATENTS drum comprises an interior cooling jacket; and supply 24127 2/19 Denmark and discharge pipes for a cooling medium connected to said cooling jacket and extending through said hollow 469535 12/28 Germany 957,540 2/57 Germany. Shaft ends 5 468,812 7/37 Great Britain.

References Cited by the Examiner UNITED STATES PATENTS 1 370 259 3 21 Allison 1 7 X I. Examiner.

2,466,443 4/49 Klaassen 24166 0 ROBERT C. RIORDON, Primary Examiner 

1. THE METHOD OF GRINDING MATERIAL COMPRISING THE STEPS OF FORMING A LAYNER OF MOVABLE GRINDING ELEMENTS IN AN ANNULAR SPACE WHOSE INNER AND OUTER PERIPHERIES ARE DEFINED BY A PAIR OF RADIALLY SPACED, COAXIAL, CIRCULAR CYLINDRICAL WALLS; ACCELERATING SAID WALLS AT THE SAME RATE TO THE SAME PREDETERMINED ANGULAR VELOCITY ABOUT THEIR LONGITUDINAL AXES; BRAKING ONE OF SAID WALLS TO THEREBY BRING IT TO REST AND PRODUCE RELATIVE MOVEMENT BETWEEN THE GRINDING ELEMENTS; ADMIXING THE MATERIAL TO BE GROUND WITH SAID LAYER OF GRINDING ELEMENTS SO THAT IT IS GROUND BY THE RELATIVE MOVEMENT OF THOSE ELEMENTS IN RELATION TO ONE ANOTHER; AND DISCHARGING THE GROUND MATERIAL FROM SAID LAYER. 